1. Field of the Invention
The present invention relates to a fine particle substance-containing non-aqueous dispersion, in particular relates to a microgel dispersion wherein a gel consisting of a fine particle substance and a polymer is dispersed in a water-insoluble organic solvent.
In this connection, it is to be noted that the "fine particle substance" referred to herein means a substance having a mean particle diameter of 1000 .ANG. or less, especially 300 .ANG. or less.
2. Description of the Prior Art
As the representative fine particle substance-containing non-aqueous dispersions can be enumerated: electrophotographic liquid developers obtained by coating pigment particles with a resin and dispersing same in a carrier liquid; gravure ink obtained by coating pigment particles with a resin and dispersing same in an organic solvent; and the like.
Recently, the study of a magnetic fluid has been promoted and many investigations have been carried out for developing new uses of the magnetic fluid. The magnetic fluid referred to herein means a liquid high-magnetic fluid obtained by dispersing a super fine particle magnetic substance having a particle diameter of about 1000 .ANG. or less, preferably about 300 .ANG. or less, more preferably about 30-50 .ANG. stably in a solvent, said substance being provided with both fluid and high-magnetic characteristics.
Production of this magnetic fluid using the conventional process, however, involves problems to be solved such as (i) the production cost is high, (ii) the products have great, from lot to lot, differences with respect to dispersed particle diameter, dispersion stability, viscosity and magnetic characteristics, and further (iii) the dispersion stability per se is not necessarily good.
The reasons for the above (i) and (ii) seem to be attributable the fact that many manufacturing steps are used and control of each step is complicated and difficult. In addition, as the reason for the above (iii) can be enumerated the fact that the step (a) or (b) of the conventional process employed for dispersing high-magnetic oxide particles in the water-insoluble organic solvent is defective. In more detail, in the step (a), which comprises flushing the high-magnetic oxide particles obtained by the wet process in the water-insoluble organic solvent, there is required a proper solid-liquid separating operation before flushing in the case of preparing a dispersion wherein the high-magnetic oxide particle is especially a super fine one having a particle diameter of 300 .ANG. or less, and further the filtering separation or centrifugal separation employed herein is itself considerably inferior in efficiency. Consequently, the step (a) further necessitates a treating step for improving the separation efficiency which in turn deteriorates the dispersion stability. In the step (b) which comprises grinding the high-magnetic oxide particles obtained by the wet process in the water-insoluble organic solvent, on the other hand, said grinding is effected by means of a ball mill, attriter or the like, but this grinding efficiency is extremely inferior, whereby a long period of time such as several weeks is required for treating and additionally it is very difficult to reduce the dispersion phase into a particle diameter of 1000 .ANG. or less, especially 300 .ANG. or less. In addition, the step (b) is defective in that it is not adapted for the mass production of the magnetic fluid on an industrial scale.
For the purpose of eliminating these defects inherent in the usual processes, novel processes for the production of magnetic fluid have been proposed; namely a process (c) (disclosed in Japanese Laid Open Patent Application No. 65182/1979) which comprises adding alkali to an aqueous solution containing ferrous salt and ferric salt to thereby adjust the pH and form colloidal particles; then adding a specific amount of unsaturated fatty acid salt to said particles to thereby coat the colloidal particles with a mono-molecular film of unsaturated fatty acid; thereafter adding a water-insoluble organic solvent thereto for layer-separating; and recovering a magnetic fluid as an organic layer; a process (d) (disclosed in Japanese Laid Open Patent Application No. 13995/1976) which comprises dispersing iron oxide in water to assume a colloidal state; adding a water-insoluble fatty acid to said dispersion while stirring vigorously to obtain a fatty acid--adsorbed iron oxide; and dispersing said iron oxide in a water-insoluble solvent for preparing a magnetic fluid; and the like.
However, the fact is that since these processes (c) and (d) employ various steps, the problems of production cost, dispersion stability and the like are not solved. Furthermore, since this dispersion stability is not necessarily superior, the dispersoid dispersed in the water-insoluble organic solvent comes to form an aggregate immediately after the preparation as well as by the lapse of time and influences from temperatures. To sum up, the above proposed processes may be said to be disadvantageous in that they can not produce the dispersoid in the very fine particle form as intended by the inventors of the present invention.